Thanks ironass,
I did do the factory reset and reinstalled all the apps manually to make sure the were compatible.

I did some googling after posting and found a few people implying that SOD was associated with wifi.
I uninstalled JuiceDefender Plus and haven't had another SOD event.
I also uninstalled the Gmail labeller which is a bit of a shame - I paid a dollar for that too :-(
Everything else seems good.

I'm beginning to see a pattern forming with the use of Juice Defender. Weirdly, you are the 5th or 6th person in a week that has commented that uninstalling Juice Defender solved their problems.

I have never been a fan of this app, or any task killer, as in my experience they cause more problems than they solve and use more battery as forcefully closing down app's and processes in Android is counter productive.